The present invention comprises a new and distinct cultivar of hybrid pistachio (Pistacia atlantica (not patented)×Pistacia integerrima (not patented) used as a rootstock known by the varietal name ‘UCB1-D90.’ The variety ‘UCB1-D90,’ is an in vitro, single selection of the segregating controlled cross of (P. atlantica×P. integerrima) made at Davis, Calif. The purpose of the selection program was to develop rootstocks with superior tolerance to soil salts. Seedlings were tested in salt trials in the laboratory and compared to the ‘UCB1-D1’ rootstock (not patented). Those seedlings that exhibited high tolerance to various soil salts were selected. The new variety exhibits high tolerance to numerous, common salts found in the soil and irrigation water. The present variety has higher resistance to Verticillium disease than the female parent, Pistacia atlantica; and has higher cold tolerance than the male parent, Pistacia integerrima. 
The following characteristics distinguish clone ‘UCB1-D90’ from the industry standard, ‘UCB1-D1’ rootstock:                1. Greater growth and tolerance to the soil salts, calcium chloride, sodium sulfate, sodium carbonate and sodium bicarbonate.        2. Greater growth and tolerance to high levels of dissolved salts in irrigation water.        3. Earlier vegetative bud break.        4. Greater graft compatibility with commercial pistachio clones.        5. The present variety differs from rootstocks UCB1-D71, UCB1-D110, and UCB1-D154 in that the present variety is more tolerant than the industry standard rootstock, UCB1-D1, to the soil salts tested, sodium sulfate, sodium carbonate and sodium bicarbonate; but it is the least tolerant of these rootstock to these same soil salts.        